In general, imaging lenses are imperfect in design. Multiple lenses of various shapes and properties are usually intricately combined in an imaging lens to compensate for the deviations from an ideal lens, but this comes at a price of high manufacturing costs and the associated increase in complexity of the lens design. Most lenses available in the market offer a well-resolved image in the region close to the center of their field-of-view, but offer poor resolution away from the center. Therefore, obtaining a well-resolved image of a sample requires raster scanning the sample and keeping the center regions of the scanned images while discarding the portions away from the center.
Bright-field imaging is one of the most popular microscope modalities. A bright-field microscope typically illuminates a specimen with white light and captures an image of the transmitted light. Bright-field image phase contrast offers information about sample structure. In combination with phase contrast methods, one may quantitatively measure sample absorption, thickness, and dispersion. Another increasingly important microscope modality in biology is fluorescence imaging. Fluorescence can help visualize chemical compositions and structures at a molecular level through appropriate labeling with fluorophores. By illuminating a tagged sample at the fluorophores' excitation light and imaging at the fluorophores' emission wavelength, biologists can easily identify labeled regions exhibiting chemical properties of interest. Combining a bright-field and fluorescence image allows one to locate fluorescing regions relative to the specimen's underlying structure.